switching devices should be separated as far as possible from data system equipment and conductors. The
architectural arrangement of the facility should allow for the maximum distance between these devices and the
data systems. This requirement also applies to heating, ventilating, and air conditioning equipment which
utilize electric motors and high amperage switching devices. The maximum distance will be limited by the
voltage drop which can be tolerated in feeders to the system equipment.
Use squirrel cage induction motors, which do not utilize slip rings or commutators, wherever
Where necessary to specify motors with commutators, specify those properly designed to minimize
arcing. Arcing at the commutator or slip rings can be decreased by careful mechanical design such as requiring
adequately sized shafts and bearings which maintain concentricity to minimize brush bounce and vibration.
1.9.2 Instrumentation Considerations. Where transducers and associated processing devices are to be installed
as an integral part of a facility, the instrumentation system must be designed and installed such that it does not
compromise the single-point signal ground networks used by other lower frequency systems. In particular,
where the systems interface, care must be utilized to assure that the grounding integrity of each is maintained.
Derive the ac power for the test equipment from the same branch circuit supplying the equipment or system
being measured. If this practice raises system reliability problems, low amperage breakers or fuses should be
provided for the test equipment outlets. If the outlets for test equipment cannot be connected to the branch
circuits feeding the primary equipment, then the test equipment branch circuit should be restricted only to test
equipment use. In particular, rotating machinery, industrial machines, appliances, vending and office machines,
and any other non-EM1 protected equipment should not be connected to that branch circuit.
1.10 EMP PROTECTION. EMP protective measures are based on intercepting the incident energy and
dissipating it or reflecting it away from the threatened device, equipment, or facility. These measures are
implemented by providing adequate metal shielding around the facility (or the equipment inside); by installing
fast response surge arresters on power, signal, and control lines; by terminating the shields and arresters in an
earthing connection offering a low impulse impedance; by carefully controlling the points of penetration of
collectors; and, finally, by paying particular attention to all bonds throughout the protective system.
1.10.1 Earth Connection. A radial, or star, configuration is preferred to other types of earth electrode
subsystems because of its lower impulse impedance (see Volume I, Section 2.6.3). Where EMP protection is to
be provided in addition to conventional signal and safety protection, supplemental radials may be added to the
One low-impulse impedance radial should be placed at each location where there are over voltage arresters or
protectors on incoming external lines or conductors. An example of such a location is the point where
commercial power lines enter the first stepdown transformer. Another location is at the point where external
conductors enter the shelter itself and where protectors or arresters are located.